3,5-Dimethylpyrrole-2,4-dicarboxylic acid 2-t-butyl ester-4-ethyl ester

1694-31-1

141-97-9

86770-31-2

1. a solution of tert-butyl acetoacetate (31.65 g, 200 mmol) in acetic acid (40 mL) was cooled to 5 °C in an ice bath. 2. slowly inject the NaN02 solution (14.00 g dissolved in water) into the reaction mixture over a period of 20 minutes, maintaining an internal temperature of no more than 15°C. The syringe was washed with water (2 x 3mL) and the wash solution was added to the mixture. 3. The reaction mixture was stirred on a melting ice bath in an open flask overnight (16 hours). 4. In another 3-necked 1L round-bottomed flask equipped with a large egg-shaped stirring bar, an internal thermometer, and a dosing funnel, anhydrous sodium acetate (20 g) and ethyl acetoacetate (29.0 g, 1.1 eq.) were dissolved in 100 mL of acetic acid and placed in an oil bath at 60 °C. 5. Zn powder (10 g, Aldrich, <10 μm) was added with vigorous stirring, followed by dropwise addition of the nitrosation mixture (from Steps 1-3). The dropwise addition process was continued for 45 min while the remaining Zn powder (40 g, ~5 g at a time, at intervals of a few minutes) was added in portions, keeping the internal temperature of the flask below 85 °C. 6. The addition funnel was washed with acetic acid (3 x 10 mL), the washings were added to the mixture and stirring was continued for 1 h at 60 °C. 7. Dilute the reaction mixture by adding 100 mL of water and continue stirring at 60 °C for 1 hour. 8. Pour the reaction mixture into a large beaker, dilute with 0.5 L of water, add crushed ice (total mixture volume of 1.5 L) and place on an ice bath and stir for 1 hour. 9. The precipitate was collected by filtration, washed thoroughly with water and dried by suction. 10. The crude product was dissolved in a mixture of ethanol and ethyl acetate (1:1, 0.5 L), heated gently, filtered to remove the remaining Zn powder and the filtrate was evaporated to dryness. 11. Suspend the solid residue in 60mL of acetonitrile and place in a refrigerator (-20°C) overnight. 12. The precipitate was collected by filtration, washed with cold acetonitrile, dried by suction and dried under high vacuum to give a white sugar-like crystalline solid (35.55 g, 66.5%). 1H-NMR (CDCl3,400MHz): δ 8.93 (br s, 1H), 4.29 (q, J=7.1Hz, 2H), 2.53 (s, 3H), 2.50 (s, 3H), 1.57 (s, 9H), 1.36 (t, J=7.1Hz, 3H).